1. Field of the Invention
The present invention relates to a method for operating a heating group subsystem in a machine for the production or treatment of a fibrous web, for example a paper or cardboard web. The invention also relates to a heating group subsystem in a machine for the production or treatment of a fibrous web, for example a paper or cardboard web.
2. Description of the Related Art
Document WO 2014/180645 A1 discloses a cascade steam system for a dryer section in a paper machine, wherein the steam pressure of the heating steam is higher in the first heating group than in the second heating group, and the steam pressure of second heating group is higher than the steam pressure in the third heating group. The heating system is arranged such that the steam pressure of the heating groups increases in machine direction. A thermo-compressor is provided to reduce the energy consumption. The thermo-compressor increases the vapor pressure in the last heating group to such an extent that it can again be fed to the heating group system in the form of heating steam.
Document AT384254 B also describes a cascade steam system for a dryer section of a paper machine wherein the steam pressure of the heating steam in the first heating group is higher than in the second heating group, and the steam pressure of the second heating group is higher than the steam pressure in the third heating group. The heating group system is arranged such that the steam pressure of the heating groups increases in the machine direction. The vapor of the heating group with the lowest pressure level is condensed in a heat exchanger for heating of the machine air, and an auxiliary condenser.
What is needed in the art is a heating system with improved energy efficiency and a more flexible mode of operation, as well as providing reduced energy consumption for the drying of paper.